At first Carlson, who was on a five-day hike on the island, thought it was a bunch of seals playing in the surf as fur seals and sea lions are quite common on Stewart Island.

When they realized the horror of what they were seeing, they dropped everything and ran straight into the water.

“We were pushing and trying to shove and drag them back out, but it was useless. They were so big and heavy, and so many of them,” Carlson told CNN. “Some were maybe 5-6 meters long, and even the babies were over a meter and all very heavy.”

“It was actually quite dangerous as they were moving so much and I got a few good whacks before we realized there was no way us two could re-float them.”

Unable to save them, Carlson’s friend, Julian Ripoll, went to contact rangers at the Department of Conservation (DOC), a prohibiting 9-mile (15-kilometer) walk in soaking wet cold and sandy clothes.

Carlson stayed with the whales until dark. She spotted a baby whale, and desperately attempted to save it.

“Once I was alone with the whales, I tried dragging a baby whale back out a few times. It was the one that was most out of the water. I tried three times, but it kept rebeaching,” she said.

“I then realized the hopelessness of it all and started to scream and cry. “I stayed with them, touching their heads and looking at them, throwing water on them and just saying sorry.”

Alerted by Ripoll, rangers could only assess the situation and come back in the morning. Ripoll and Carlson, who went back to the camp that night, also returned to the beach the next morning.

Carlson said the scene they encountered was appalling.

Half of the whales were already dead, half-sunk in the sand, and the remaining animals had to be euthanized, according to the DOC.

The remoteness of Stewart Island, a sparsely populated island in the country’s south, and the condition of the surviving whales meant it was impossible to save the whales, even with the right equipment, Stewart Island operations manager for the DOC Ren Leppens, said. He added that the decision to euthanize the remaining whales was “heartbreaking.” As many as 145 whales have died in the mass stranding, the DOC said.

In two unrelated strandings over the last few days, nine pygmy killer whales and another 41 pilot whales died in New Zealand, according to the Associated Press.

In an Instagram post, Carlson later expressed her feelings of desperation and futility in front of such tragedy.

“I’ll never forget their cries, the way they watched me as I sat with them in the water, how they desperately tried to swim but their weight only dug them deeper into the sands,” she wrote. “I sank to my knees in the sand screaming in frustration and crying, with the sound of dozens of dying whales behind me, utterly alone.”

The exact reasons why whales and dolphins become stranded are not fully understood. Contributing factors can include “sickness, navigational error, geographical features, a rapidly falling tide, being chased by a predator, or extreme weather,” the DOC’s statement said.